It is known that the vacuum from the intake manifold of an automobile engine is always changing under different load or speed conditions of the engine, and is also changing as a function of the torque which occurs with the turning of the engine.
The present applicant filed an application for his earlier invention and was granted a patent (U.S. Pat. No. 3,834,359) therefor. In that patent, he claimed a method of and an apparatus for minimizing the amount of noxious gases from the engine by injecting a controlled amount of water into the combustion chamber in proportion to changes in the intake vacuum. Recently, he has discovered from experiments that the supply of water is particularly effective for minimizing the amount of nitrogen oxides(NO.sub.x ) that increase as the engine speed is accelerating and constant, and the supply of air is particularly effective for carbon monoxides (CO.sub.x) and hydrocarbons(HC) which increase as the engine speed diminishes. This means that the supply of water is not important for nitrogen oxides the production of which is negligible when the engine speed diminishes. From the above observation, he has developed effective and economical improved means of controlling the production of noxious gases such as carbon monoxides (CO.sub.x), nitrogen oxides(NO.sub.x ) and hydrocarbons(HC) particularly by injecting proper amounts of water and/or air into the combustion chamber. In order to realize such improved means, then, he has sought the type and amount of these noxious gases that are produced under different load or speed conditions of the engine such as idling, accelerating, normal and slow-down, and obtained the results for each type of engine condition which will be described hereinafter.
The quantities of water and/or air to be injected were determined on the basis of these results and controlled in response to changes in the intake vacuum. Therefore, two valve means for water and air were provided which were automatically actuated to open and close in response to such changes in the intake vacuum. In his further study of the improved means, however, he has encountered a problem since in the improved means, too large an amount of water must be used for minimizing the amount of noxious gases such as nitrogen oxides in particular and this requires a large-sized apparatus. It has also been revealed that the supply of water cannot be controlled when a lower intake vacuum condition continues when the engine is out of order or during cold winter days, for example, resulting in a larger amount of water being injected.